LIMA (REUTERS).- Archaelogists say scrawl on the back of a letter recovered from a 17th century dig site reveals a previously unknown language spoken by indigenous peoples in northern Peru.

A team of international archaeologists found the letter under a pile of adobe bricks in a collapsed church complex near Trujillo, 347 miles north of Lima. The complex had been inhabited by Dominican friars for two centuries.

"Our investigations determined that this piece of paper records a number system in a language that has been lost for hundreds of years," Jeffrey Quilter, an archaeologist at Harvard's Peabody Museum of Archaeology and Ethnology, told Reuters.

A photograph of the letter recently released by archaeologists shows a column of numbers written in Spanish and translated into a language that scholars say is now extinct.

"We discovered a language no one has seen or heard since the 16th or 17th century," Quilter said, adding that the language appears to have been influenced by Quechua, an ancient tongue still spoken by millions of people across the Andes.

He said it could also be the written version of a language colonial-era Spaniards referred to in historical writings as pescadora, for the fishermen on Peru's northern coast who spoke it.

So far no record of the pescadora language has been found.

The letter, buried in the ruins of the Magdalena de Cao Viejo church at the El Brujo Archaeological Complex in northern Peru, was discovered in 2008.

But Quilter said archaeologists decided to keep their discovery secret until the research showing evidence of the lost language was published this month in the journal American Anthropologist.

"I think a lot of people don't realize how many languages were spoken in pre-contact times," Quilter said. "Linguistically, the relationship between the Spanish conquistadors and the indigenous was very complex."

(Reporting by Emily Schmall; Editing by Patricia Reaney)